The present invention relates generally to instrumentation used in turbine power plants and development test turbines and, more specifically, to a total-pressure probe effective in high-moisture conditions.
Total-pressure probes are often used to measure total pressure in a fluid environment where the direction of flow is not known or changes with operating conditions. Kiel-style probes have a straight flow-through design and are typically installed on cylindrical rake masts. These probes are mounted at various radial locations across a flow path, and pressure tubing is routed through the rake mast to a transducer where the pressure measurement is translated to a signal for routing to a data acquisition system.
The Kiel-style probe is a pitot-style probe but has a shroud to protect the pressure tubing. The shroud makes the probe insensitive to a range of yaw and pitch angles because the flow is straightened as it enters the probe. Kiel-style probes are sometimes installed in the exhaust duct of, for example, a low-pressure steam-turbine section during performance testing to measure the total pressure distribution exiting the last-stage row of buckets. U.S. Pat. No. 4,433,584 discloses a plurality of Kiel-style probes on a rake downstream of a turbine section, described in further detail below.
Measuring total pressure in a wet-steam environment, however, is often hampered by the development of water “legs” in the pressure tubing. Because of the long length of the pressure tubing, the length of the water legs is often unknown. Without this information, it is impossible to recalculate the correct pressure measurement. The exact mechanism by which water legs are formed is unknown, but one theory is that the wet steam impinges on the pressure tubing and is forced into the tubing. Dry air is often used to purge the pressure tubing of moisture, but the effects of adding a large amount of air to the exhaust can also affect the accuracy of the pressure measurements. It would therefore be desirable to develop a mechanism that more effectively prevents the build up of moisture in the pressure tubing and the attendant formation of water legs.